Stumped! Horn doesn't work 2012 Sienna

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Oct 12, 2010
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Hey folks,

I had the grille off my 2012 Sienna to replace the radiator and afterward the horns quit functioning. I went to troubleshoot it tonight and am at a complete loss. I would appreciate any ideas of input about this.

Here's what I checked so far:

Both horns measure 1.4 ohm and will sound when jumped to the battery
Both horn connectors get a healthy 12V when the horn button on steering wheel is pressed (key off or on)
Circuit diagram below. I inspected the P/I 40A and the ECU-IG1 10A fuses and they are fine
All contacts cleaned and sprayed with de-oxit
Finally, I tried plugging in a horn and jumping the ground direct to the negative terminal. Does not sound
I'm not 100% sure where the A1 and A2 grounds are but all the grounds in that area I can see seem fine.
I did not look for the horn relay. But based on the fact that I'm getting 12V I don't think that's the problem?

Screen Shot 2022-10-17 at 10.46.57 PM.jpg


Thank you!
 
Can you get your test leads on the connector with the horn installed? It's almost like you have a broken wire that's losing connection at a certain bend.
 
Both horn connectors get a healthy 12V when the horn button on steering wheel is pressed (key off or on)

That means little unless you are testing the horn connectors for 12V with a horn plugged into them.

A typical multimeter has a 10 megohm impedance and will read 12V through very high resistance. Try putting one probe to ground, put one probe in your hand, and touch the positive battery terminal. I bet you read 12V right through the resistance of your body.
 
You're testing for voltage with the Horns unplugged? If so check for voltage with them plugged in. Voltage on a unloaded circuit doesn't mean anything.

You can make your own circuit loading test light with a H11 headlight bulb which draws close to 5 amps.
 
Can you get your test leads on the connector with the horn installed? It's almost like you have a broken wire that's losing connection at a certain bend.
Yes -- 12V from connector to battery negative
 
You're testing for voltage with the Horns unplugged? If so check for voltage with them plugged in. Voltage on a unloaded circuit doesn't mean anything.

You can make your own circuit loading test light with a H11 headlight bulb which draws close to 5 amps.
So you're saying to check that the horn connectors will put out some current, not just read 12V when the horn is pressed. OK, I can try that.
 
That is puzzling!

You've ruled out bad horns and bad grounds by being able to make the horns work when you apply 12 V directly to the inputs.

That must mean that the 12 V supply to the horns is, in some way, defective.

I like @clinebarger 's idea of using an old sealed-beam headlight as a load - it approximates a horn loadwise, and will give you a visual indication of whether enough voltage and current is reaching the horns.
 
That is puzzling!

You've ruled out bad horns and bad grounds by being able to make the horns work when you apply 12 V directly to the inputs.

That must mean that the 12 V supply to the horns is, in some way, defective.

I like @clinebarger 's idea of using an old sealed-beam headlight as a load - it approximates a horn loadwise, and will give you a visual indication of whether enough voltage and current is reaching the horns.

Yes I will try the load test as suggested. What would this point to if it fails the test? Is it likely that both horns failed simultaneously, even through they work when jumped to the battery? Relay?
 
Yes I will try the load test as suggested. What would this point to if it fails the test? Is it likely that both horns failed simultaneously, even through they work when jumped to the battery? Relay?

It very well could be the relay. Perhaps the contacts inside are burned and not making a good connection. You could try using a jumper wire in place of the relay and see if that makes the horns work.
 
It very well could be the relay. Perhaps the contacts inside are burned and not making a good connection. You could try using a jumper wire in place of the relay and see if that makes the horns work.
I am struggling to determine which relay belongs to the horn. I even have the FSM. I gotta say, the FSMs for these newer vehicles are pretty much junk. The ones from the 80's and 90's were written to be understood...
 
I am struggling to determine which relay belongs to the horn. I even have the FSM. I gotta say, the FSMs for these newer vehicles are pretty much junk. The ones from the 80's and 90's were written to be understood...

You should hear one clicking when you push the horn button. And you can usually feel it click if your finger is on it when you push the horn button.

There is usually a diagram that shows what all the relays are for. It's often even in the owner's manual.
 
Yes I will try the load test as suggested. What would this point to if it fails the test? Is it likely that both horns failed simultaneously, even through they work when jumped to the battery? Relay?
But given that the horns work when you run a 12 V feed to them directly, it doesn't seem like they're the problem.
 
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I am struggling to determine which relay belongs to the horn. I even have the FSM. I gotta say, the FSMs for these newer vehicles are pretty much junk. The ones from the 80's and 90's were written to be understood...
Agreed, it's not as simple a circuit as I would have expected or hoped for.

The simplest horn circuit I can imagine would have the one side of the horn tied to ground, and the other tied to the open side of a normally open momentary-contact switch (the horn switch). The other side of the switch would be tied to 12 V. When you depress the horn button (i.e. close the switch), you would allow current from the 12 V source to flow though the switch, out to the horn, and through the horn to ground.

Alternatively, and equally simple, the one side of the horn would be tied permanently to 12 V, and the switch would ground the other side, again allowing current to flow through the horn.

But given the relatively heavy current draw, a horn relay is typically used; the horn button or switch, still normally open, would allow low current to flow through the primary winding of the horn relay, closing a heavier current switch, allowing heavier current to flow through the horn.

But in this case, the horn switch completes a ground, which appears to complete the horn circuit in the horn portion of the ECU and/or the engine room junction box. And yet, the low side of the horns are also grounded, so the circuit is obviously not continuous.

If this were a Dodge Grand Caravan, I would suspect the clockspring, but given that it's a Toyota Sienna, and given that the problem is coincident with your work under the hood, I suspect it would be something in the wiring between the underhood junction box and the horns.

I would be tempted to run 12 V to the GRN/WHT wire which runs from the Integration Relay (Pin C5) and see if the horns operate. If not, your problem is downstream (toward the horns). If so, the problem is upstream.

Good luck, and please keep us posted.
 
Update: tried the panic button. Lights flash and stuff but horns don't honk. I don't have a security system on it (which would come with an extra little horn).
 
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